We use scaled 3-D thermo-mechanical analogue models to investigate the formation of oroclines (originally linear orogens now curved in map view by buckling about vertical axes). The experimental setup consists of a tank of water (the asthenosphere) on top of which rest hydrocarbon plates (the lithosphere) with strain-softening behaviours and thermo-dependent elasto-plastic properties. An electric heating element below and 4 infrared lights above produce a constant vertical (geo)thermal gradient in the plates. A horizontal piston drives constant plate motion and gives rise to a compressional stress regime. Geometric, kinematic and dynamic variables are calibrated in accordance with a set of scaling laws and proper plate composition. Our results suggest that oroclinal buckling involves the entire lithosphere and cannot be confined to the crust only. A wide range of syn-oroclinal structures developed during buckling, including thin- to thick-skinned thrust belts, transform faults and extensional structures, as well as extensional basins and subduction zones in the lithosphere adjacent to the ribbons. During oroclinal buckling, a thrust belt forms upon complete closure of the interlimb region and is attributable to the trailing orocline limb overthrusting the leading orocline limb. An analogous syn-oroclinal thrust system characterizes the Central Iberian Orocline (CIO) of the Variscan orogen in Iberia where the north limb of the west-convex orocline exposes recumbent north-verging folds while the overriding south limb bears upright to gently north-verging folds. Our results imply that these structures developed during final closure of the CIO, and indicate that the north- and south- limbs of the CIO constitute the leading- and trailing-limbs, respectively, of an orocline that formed by overall northward translation. Modelling of magmatic arcs rotating about vertical axes yields late stage transform faults that bisect the buckling arcs. This outcome is analogous to the Panama Canal fault zone that severs the buckled Panamanian Isthmus. The hinge zones of modeled oroclines are the sites of subduction initiation, similar to subduction initiation of the Caribbean plate beneath the convex to the north, North Panamanian orocline, and of oceanic lithosphere from the Ionian Sea beneath the Calabrian orocline of Sicily. / Graduate / 0372 / gagnonl@uvic.ca

This thesis discusses the effects of basal friction and basement configuration on the deformation of the fold-and-thrust belts in convergent zones. A series of analogue models were conducted with adjacent different basal configuration and frictional properties to observe and gain a better understanding of these basal effects and their interactions. The results from these side-by-side systematic models demonstrate that the kinematics and geometry of the deformation wedges are strongly influenced by the mechanical and geometrical basal effects. In these experiments, high accuracy laser scanner and digital camera were used to record the evolution of the surface topography of the deformed sand packs. Comparison between models with different basal friction shows that the basal friction plays a significant role on the propagation and topography of the deformation structures in aspects such as wedge height, taper angle, number of imbricates and deformation front. The models with a basal viscous material, which acts as low friction substrate, illustrates that the propagation of deformation above viscous material is faster and further than above the adjacent mechanically different frictional decollement. In the experiments with a moving plate under the part of the sand pack, the velocity discontinuity was introduced by either rigid, i.e. frontal edge of the metal plate, or deformable like distal end of the viscous materials. The results of these kinds of experiments, applicable to for example basement faults, salt decollements and tectonic underplating simulations, illustrate that the deformation localizes and develops continuously above the velocity discontinuities. Besides, the different rate and distance of the propagation of deformation fronts caused by different substrate distribution between the adjacent zones also lead to the formation of transpressive zones at the boundary of these adjacent domains with different basal friction/configurations.

Flow-like mass movement is the most destructive landslide and causes loss of lives and substantial property damage throughout the world every year. This thesis focuses on the spatial and temporal changes of the mass movement in terms of velocity and displacement within the failure mass, and the spatial and temporal distribution of the three dimensional internal deformation of the granular slopes using discrete element method, physical experiments, and natural landslides. We have also studied the effect of weak horizons on the kinematics and internal deformation of granular slopes. Numerical model results show the following features related to a failure mass. The failure mass flows downwards in an undulating pattern with a distinctive velocity heterogeneity. Dilatation within the failure mass is strongly dependent on its mechanical properties. A larger mass moves downslope and the mass moves faster and further in the model with lower internal friction and cohesion. The presence of weak horizons within the granular slope strongly influences displacement, location of the failure surface, and the amount of the failure mass. In addition, results from analogue models and natural landslides are used to outline the mode of granular failure. The collapse of granular slopes results in different-generation extensional faults in the back of the slope, and contractional structures (overturned folds, sheath folds and thrusts) in the toe of the slope. The first-generation normal faults with a steep dip (about 60º) cut across the entire stratigraphy of the slope, whereas the later-generation normal faults with a gentle dip (about 40º) cut across the shallow units. The nature of the runout base has a significant influence on the runout distance, topography and internal deformation of a granular slope. Good agreements are found between models and nature for the collapse of granular slopes in terms of the similar structural distribution in the head and toe of the failure mass and different generations of failure surfaces. The presence of a weak horizon within the granular slope has a significant influence on the granular failure and three dimensional internal deformation of the failure mass.

Dans ce manuscrit nous développons l'approche cinématique 2D du calcul à la rupture pour examinerles effondrements en extension (ou failles normales) de la croûte supérieure cassante qui résultent desurpressions de fluides. Les sujets d'intérêt liés à la déformation en extension sont (1) les roles de lapression des fluides, des processus de surface, et des propriétés des matériaux et des failles sur lastabilité des structures d'extension; (2) la formation de failles normales à faible pendage et de failleslistriques; (3) la distribution de la déformation au dessus d'un glissement à faible pendage; et (4)l'influence de l'adoucissement mécanique des failles et des processus de sédimentation sur cettedistribution.Cette approche mécanique est vérifiée par la théorie du prisme critique de Coulomb, et la généralise pour étudier la topographie complexe de la péninsule de Mejillones dans le Nord du Chili. Cetteapproche est aussi appliquée à l'instabilité gravitaire dans le delta du Niger en reliant les structurescompressives en bas de pente aux structure extensives en amont par un détachement profond. Nousprédisons des surpressions de fluides beaucoup plus élevée que celles obtenues par application duprisme de Coulomb. Enfin, cette méthodologie est appliquée à l'étude de la forme de failles normalesreliant un détachement profond à la surface. Dans le cas du delta du Niger, nous montrons que lesfailles à faible pendage et les failles listriques impliquent que la profondeur de rétention des fluides estfaible. La version séquentielle de l'analyse limite ouvre de nouvelles voies pour suivre l'évolutionstructurale dans le temps du jeu sur les failles normales. Les simulations montrent en particulier qu'unefaille normale tourne vers des pendage plus faibles au fur et à mesure de la dénudation du mur, formantune région qui passe du mur au toit de la faille active en rotation. La prédiction de cette région estillustrée par des expériences analogiques et des exemples de terrain. / This manuscript develops a 2D kinematic approach of Limit Analysis to examine the extensionalfailures in the brittle, upper crust resulting from fluid overpressures and normal faulting. There aremany interesting topics related to the extensional deformation such as (1) the roles of fluid pressure,topographic process, material and fault properties on the stability of extensional structures; (2) theformation of low-angle and listric normal fault; (3) the deformation pattern due to slip on a low-anglefault; and (4) the influence of fault softening and sedimentation processes on this deformation pattern.This mechanical approach applied to wedge prototypes is validated by the critical Coulomb wedge(CCW) theory, and it generalizes the CCW theory to investigate the complex topography on theMejillones peninsula, Northern Chile. Additionally, this approach is also applied to investigate gravityinstability of Niger Delta by linking down-slope compressional to up-slope extensional failures througha deep detachment. We predict much higher fluid overpressures than that of the CCW theory. Finally,this Limit Analysis methodology is applied to investigate the shape of normal fault linking a lowdetachment to the surface. The application to Niger Delta implies that the formation of very low-angleand strongly listric faults results from a shallow fluid-retention depth. The sequential version of LimitAnalysis opens new ways to envision the structural evolution through time resulting from normalfaulting. The simulations show that the normal fault rotates during extension, forming a region of Footto-Hanging Wall (FHW) where the material in the footwall is sheared upon entering the hanging wall.The creation of the FHW region is illustrated by sandbox experiments and field examples.